Laboratory apparatus



United States Patent I O 3,403,982 LABORATORY APPARATUS Rudolph B. Fricioni, Cheswick, Pa., assignor to Allegheny Ludlum Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania No Drawing. Filed Mar. 18, 1964, Ser. No. 352,985 2 Claims. (Cl. 23-292) ABSTRACT OF THE DISCLOSURE An article of manufacture is described in which zirconia, iron and copper are employed in the production of a nonporous sintered crucible suitable for use in a combustion analyzer. There is also described a sintered zirconia crucible which is provided with a lining of a reaction product of a mixture of iron and copper components for sealing the pores and the method for producing the same.

This invention relates to laboratory crucibles, and in particular to laboratory crucibles which are particularly suited for use in a combustion analyzer.

The combustion analyzer is now widely used and has become comparatievly standard in industry for the analysis of a wide range of combustible materials containing sulfur and carbon. During the analysis of these combustible materials for the determination of the amounts of carbon and sulfur contained within said combustible ma terials, predetermined amounts of the material to be analyzed are placed in a crucible which is then inserted into a combustion tube, heat is applied to the materials being analyzed, and the sulfur and/ or carbon which is evolved is separated, collected, and the amount thereof determined by well-known means. Since the material from which the crucible is made must be substantially free of the components for which it is desired to make the analytical determination, the industry has recognized that sintered zirconia offers refractory ware having the lowest possible blanks for both sulfur and carbon. When zirconia is sintered during the manufacture of said crucibles, it has been found that the crucibles are porous with the result that the required high temperatures necessary for the evolution of both carbon and sulfur are not readily obtained without either damage to the crucible or associated equipment. As a result, it has not been feasible to obtain a calibration curve for use with the combustion analyzer in order to obtain the desired degree of accuracy in carbon and sulfur determinations employing said fusion technique.

An object of the present invention is to provide a method for sealing the pores of zirconia crucibles which will permit the use of higher temperatures in a standard combustion analyzer, thereby obtaining more accurate results.

Another object of this invention is to provide an article of manufacture for use with a combustion analyzer for the accurate determination of sulfur and carbon.

A further object of the present invention is to provide a new article of manufacture comprising a crucible having a composition containing a major amount of zirconia and minor amounts of iron, copper and components thereof for use a with a combustion analyzer.

Other objects of the invention will be apparent to one skilled in the art when read in conjunction with the following description:

In its broader aspects, the invention contemplates a crucible for use with a combustion analyzer, which crucible is formed from a composition having a major amount of zirconia and minor amounts of one or more finely divided components selected from the group consisting of iron, copper, iron compounds, copper com pounds and mixtures thereof, each of said components Patented Oct. 1, 1968 being substantially free of sulfur, carbon and components thereof/The present invention also contemplates an article of manufacture which consists of a commercially available sintered zirconia crucible having a fused lining contained therein, said fused lining being formed from the reaction of fluxing one or more of the finely divided components selected from the group consisting of iron, copper, iron compounds, copper compounds and mixtures thereof.

Furthermore, the invention also contemplates the method of analyzing for carbon or sulfur wherein a standard, commercially available, porous, sintered zirconia crucible is first heated to a temperature within the range between 2400 F. and 2800 F., while containing one or more of the components selected from the group consisting of iron, copper, iron compounds, copper compounds and mixtures thereof, each of said components being substantially free of sulfur, carbon and components thereof, to form an adherent fused lining in said crucible thus sealing the pores, cooling the crucible and thereafter employing said crucible in a combustion analyzer for the determination of carbon or sulfur in combustible materials.

In particular, it has been found that the use of the presently commercially available sintered zirconia crucibles has resulted in erratic results, especially in the determination of sulfur contained in steels having less than 0.01% sulfur present therein. It has been determined that the reason for these inaccuracies results from the fact that the commercially availabe sintered zirconia crucibles have an operating temperature which should not exceed about 2300 F. For the proper determination of sulfur, it is deemed expedient that the materials to be analyzed, should be heated to a temperature of at least 2600 F. in order to obtain substantially complete evolution of sulfur from the material being tested. Attempts to increase the relative operating temperature of the known zirconia crucibles have resulted in either a burn through of the crucible or in thermal damage to the crucible upon cooling so that the known crucibles have an exceedingly short life. It has been found that the life of the crucible can be materially increased by factor of about 3 where the crucible is provided with a fused lining which is effective for sealing the pores which are inherent in the sintered zirconia crucible. Where substantially pure iron or compounds thereof and/or substantially pure copper or compounds thereof are fused to form a lining within and over the inner surfaces of said zirconia crucible, it has been possible to operate the lined crucible at a temperature of approximately 2800 F. to 2900 F. In addition, it has been found that where a commercially available sintered zirconia crucible has been lined as taught herein by the fusion of iron, copper, iron compounds, copper compounds or mixtures thereof, such a coated or lined crucible can be employed for at least three times the number of determinations as the unlined crucible. Moreover, with the use of the higher operating temperatures, the evolution of carbon or sulfur, whichever is to be determined, is more complete resulting in greater accuracy for each determination irrespective of the fact that the crucible has been used one, three or five times previously.

As a specific example, a standard commercially available sintered zirconia crucible, i.e. a crucible like that illustrated in United States Patent No. 2,930,602, was employed and was lined utilizing a mixture of copper oxide and low carbon (less than .03%) iron containing about 3% silicon and which mixture is substantially free of carbon, sulfur or components thereof. A quantity of this mixture consisting of /2 gram of the iron and /2 gram of the copper oxide was placed within the crucible after which the crucible was heated to a temperature of about 2600 F. until fusion took place and the crucible was then inclined and rotated to form a lining of the fused mixture on the inner surface of the crucible. The fused metal lining thus formed seals the pores and provides better coupling when used in the high frequency furnace of the combustion analyzer. The lining thus formed should have a thickness ranging from a minimum of 0.5 mm. to a maximum of 2 mm. In the present example the fused lining measured about 1 mm. in thickness. Thereafter the crucible was cooled to room temperature and employed in a standard combustion analyzer i.e., model No. 521 Leco. This lined crucible was employed for a total of determinations. At the same time a standard, commercially available crucible without any lining, was also employed in the same combustion analyzer for the same determination of sulfur. After the initial determination, the unlined conventional crucible had to be discarded. Moreover, the differences in the determinations varied by a factor of for each unlined zirconia crucible analyzing material from the same sample, whereas the differences in the sulfur determination on the same sample employing the method of the present invention, varied by a factor of experimental difierence only.

As an alternative to employing the standard commerciallly available sintered zirconia crucible and providing a lining therein, as taught hereinbefore, the present invention also contemplates a new article of manufacture. This article of manufacture is a laboratory crucible substantially similar in shape to that shown in United States Patent No. 2,930,602, but being formed of a composition containing a major amount of zirconia and minor amounts of one or more of the components selected from the group of iron, copper, iron compounds, copper compounds and mixtures thereof, which are substantially free of sulfur, carbon and components thereof, said minor components comprising from about /2 to about 3% by weight for zirconia present. In this respect, the crucible can be formed by employing a major amount of zirconia and minor amounts of, for example, copper and ironcarbonyl. This mixture is formed to the shape of a crucible suitable for use in a combustion analyzer and fired to sinter the components into the rigid form of the crucible. As thus sintered, the crucible is substantially nonporous and can be used at said elevated temperatures, i.e. at temperatures of about 2800 F. for the determination of sulfur. This article of manufacture, since it has no lining per se and a larger usable volume is therefore presheating the components, as taught hereinbefore, as will be evident when one considers that as successive determinations are made, materials are added to the materials previously analyzed in the same crucible.

Crucibles produced in accordance with and embodying features of the present invention have been successfully utilized in the determination of carbon or sulfur wherein the fusion technique is employed in a combustion analyzer and the results have shown a surprising degree of accuracy. Moreover, such crucibles can be employed or reused a great number of times in a combustionanalyzer, thus resulting in substantial savings in laboratory equipment alone. In addition, the metallic components of the lining or in the structure of the crucible itself porvide improved coupling in the high frequency furnace of the combustion analyzer thereby increasing the output or efliciency of this equipment. Moreover, there are no special skills required, nor techniques invoved in practicing the process of the present invention, nor in the manufacture of the article of the present invention as described hereinbefore.

I claim:

1. An article of manufacture for use in the chemical analysis of carbon and sulfur, comprising a sintered crucible having a nonporous inner surface and being of a composition consisting of a major amount of zirconia and minor amounts of one or more of the components selected from the group consisting of iron, copper, iron compounds, copper compounds and mixtures thereof, each of said components being substantially free of sulfur, carbon and components thereof.

2. An article as defined in claim 1 wherein said nonporous inner surface is a lining bonded integrally to the remainder of said crucible.

References Cited UNITED STATES PATENTS 401,097 4/1889 Anderson 106-55 1,482,887 2/1924 Collins 26348 3,180,632 4/1962 Katz et a1. 26348 1,884,665 10/1932 Greiner 117123 XR 3,136,658 6/1964 Richards 117-123 XR MORRIS O. WOLK, Primary Examiner.

R. E. SERWIN, Assistant Examiner. 

